Vehicle climate control systems, or heating systems, may use coolant to provide cabin heat, and may further provide such coolant flow to multiple locations of the cabin, such as the, front, rear, left side, right side, etc. In some cases, during lower coolant flow (e.g., idle) conditions, the coolant flow to certain areas (e.g., to the rear cabin area of the vehicle) may be too low, and thus insufficient heat may be provided to the cabin during an extended idle condition.
One approach provides an additional pump to provide the additional flow so that such low flow conditions may be avoided. However, this may add additional system complexity and cost. The inventors herein have recognized an alternative approach may be used that increases engine idle speed during cold ambient temperature to provide the increased coolant flow to the rear cabin heating system. However, such an approach can decrease fuel economy, and increase concerns with high idle speed operation noticed by the customer.
Therefore, in one approach, a system is provided, comprising: a vehicle cabin heating system having a first and second heating system receiving coolant flow from the engine; and a control system for operating the engine at a first engine idle speed upon entering idle speed control operation from previous drive operation, maintaining said first idle speed for a duration, and then increasing engine speed to increase coolant flow to the second heating system during cold ambient conditions when the second heater system is in operation.
In this way, during normal driving conditions, while a customer drives down the road, the engine speed resulting from the drive cycle is typically high enough to provide coolant flow to the rear heater without the auxiliary pump. Then, when the vehicles comes to a stop there is typically enough thermal inertia in the heater core to provide heat for a couple of minutes, so the coolant flow can be delayed and fuel economy maintained. Yet, during those conditions of an extended low flow (e.g., extended idle), the engine speed can be increased to increase coolant flow until vehicle driving is again resumed. Thus, improved heating can be obtained while sacrificing fuel economy only during limited conditions, and while addressing vehicle drivability and high idle speed warranty concerns.